Paragons of Conformational Control in Metalloenzyme Reactivity Lisa Olshansky Project Summary. Recent decades have witnessed a revolution in what was once a static picture of biology. For example, the tenets of biochemistry once taught that sequence determines structure, but we now know that sequence and cellular environment determine conformational sampling. Evolutionary selection acts on dynamic rather than static features. The implications for this dynamic biochemical world permeate all aspects of human health. Therefore, it is essential that contemporary research explore the roles, mechanisms, and structure- function paradigms at play therein. However, the complex interplay between structural changes and changes in reactivity make exploring these paradigms in natural systems incredibly challenging. At the same time, simplified synthetic models typically fail to capture the key elements of control leveraged in Nature to regulate activity. My approach is to combine these tactics. By incorporating synthetically prepared metal complexes into proteins that have evolved to undergo allosterically driven conformational changes, we are preparing switchable artificial metalloproteins (swArMs) that represent paragons for conformational control in metalloenzyme reactivity. By creating artificial systems in which changes in structure are directly linked to changes in function, we aim to quantify the effects of conformational control in terms of thermodynamic and kinetic parameters underlying reactivity. Ultimately, this understanding can be harnessed in the development of new catalysts, bioimaging agents, and systems for targeted drug delivery. Our work is poised for the exploration of key unanswered questions in enzyme catalysis, such as how allosteric binding events are converted into metallocofactor activation, or how entropic factors regulate radical chemistry, or how energy conversion occurs in mitochondrial respiratory proteins. Using a wide range of biophysical and spectroscopic methods, swArMs provide a platform with which to explore all of these questions, and to examine the mechanisms of regulation underlying function and dysfunction in metalloenzyme reactivity that are critical to human health.